Metastatic brain tumors now represent the most common lesion treated by Gamma Knife radiosurgery in the United States. Multiple studies confirm excellent tumor control rates (of approximately 85%) with low associated morbidity. Gamma Knife radiosurgery can be used for solitary or multiple tumors. Whole brain radiation therapy is sometimes used in addition to Gamma Knife. Gamma Knife radiosurgery is highly effective even for tumors that are relatively resistant to traditional external beam radiation therapy. Treatment with Gamma Knife appears to improve longevity and also quality of life.
Meningiomas are benign dural based tumors. They respond extremely well to Gamma Knife radiosurgery, with tumor control rates in the order of 90%. Associated morbidity is low with an excellent rate of stabilization of neuralgic status. Difficult skull base tumors and recurrent or residual meningiomas are especially suited to Gamma Knife radiosurgery.
Pituitary tumors requiring surgical intervention are generally best managed by microsurgery. Gamma Knife radiosurgery is very useful in treating recurrent or residual tumors, especially in the cavernous sinus. Tumor control rates of approximately 90% are reported with excellent preservation of cranial nerve and pituitary function.
Gamma Knife radiosurgery has an excellent track record in the treatment of Acoustic Neuromas. The medical literature sites tumor control rates that exceed 90% with very low morbidity. Even preservation of useful hearing has been seen in a high percentage of cases. In the small percentage of patients who do experience facial deficits after Gamma Knife, the deficit is often only temporary.
Gamma Knife radiosurgery has been used to successfully treat thousands of patients with AVMs. Lesions less than 4 ml in volume that are located in deep or inaccessible parts of the brain are ideal for Gamma Knife radiosurgery. There is an approximately 2 year latency period following Gamma Knife and some lesions require even more time before obliteration is seen. For AVMs that do not respond initially to radiosurgery, retreatment of the lesion can be considered as well.
Gamma Knife radiosurgery may have a role in the treatment of recurrent or residual gliomas. In patients who have had surgery followed by external beam radiation therapy, the Gamma Knife can be helpful in delivering a high boost dose to the residual or recurrent tumor. Gliomas that have been treated include glioblastomas, lower grade astrocytomas (including anaplastic), oligodendrogliomas and ependymomas.
Gamma Knife radiosurgery provides another excellent treatment option for patients with trigeminal neuralgia who fail to respond to medical therapy. It can be used as a primary modality or in patients who have not responded to microsurgical decompression or percutaneous radiofrequency lesions. The reported favorable response rate is approximately 80%.